The present invention relates to a disk drive and a control method of it and, in particular, concerns the control of a heater provided in the head slider to adjust the clearance between the head element section and the recording disk in the disk drive.
As known, there are a variety of data storage devices which use different types of media such as optical disks, magnetic tapes, and semiconductor memories. Among them, the hard disk drive (HDD) has become so popular as to be one of the indispensable storage devices for today's computer systems. Further, not limited to computers, the hard disk drive is widening its range of applications more and more due to the superior characteristics. For example, HDDs are now used in moving picture recording/reproducing apparatus, car navigation systems, cellular phones, removable memories for digital cameras and so on.
Each magnetic disk used in hard disk drives has a plurality of data tracks formed concentrically. In each data track, a plurality of servo data containing address information and a plurality of data sectors containing user data are recorded. A plurality of data sectors are recorded between servo data. Data can be written to and read from a desired data sector by a head element section of a head slider held on an actuator which is swung to access the data sector according to the address information of the servo data.
To raise the recording density of a magnetic disk, it is important to reduce the clearance between the head element section of the flying head slider and the magnetic disk. Accordingly, several mechanisms have been proposed in order to adjust this clearance. One of them is to provide a heater in the head slider and adjust the clearance by using the heater to heat up the head element section (for example, refer to Patent Document 1 (Japanese Patent Laid-Open No. 1993-20635)). In the present specification, this is called TFC (Thermal Fly height Control). TFC heats up the heater by supplying current to it, which causes the head element section to protrude due to thermal expansion. This can reduce the clearance between the magnetic disk and the head element section.
Even in normal operation, the head element section may also protrude due to thermal expansion. In normal operation, the head element section may exhibit two types of protrusions. One is attributable to the rise of the environmental temperature while the other is to the write element which heats up during data write operation. For the write element to write data to the magnetic disk, current is applied to the coil of the write element to generate a magnetic field. This write current heats up the write element.
In designing a HDD, the protrusion of the head element section attributable to the environmental temperature and that attributable to the write current are taken into consideration in order to avoid collision between the head element section and the magnetic disk. For example, it is therefore likely that the design does not realize satisfactory read performance in low temperature environment while satisfactory read performance is attained in high temperature environment.
TFC reduces the clearance between the head element section and the magnetic disk and gives a solution to such issues as the above-mentioned unsatisfactory read performance and the poor overwrite performance in the initial period of each data write operation. On the other hand, TFC may increase the possibility of collision between the magnetic disk and the head element section since the head element section is more protruded than without TFC. Therefore, controlling the timing of energizing the heater to protrude the head element section is critical in TFC.
As means to retreat HDD head sliders, CSS (Contact Start and Stop) and load/unload systems are known. In an HDD where a load/unload system is employed, a ramp is provided to retreat a head thereto from the magnetic disk surface. The ramp is located near the periphery of the magnetic disk. While the magnetic disk is stopped or the HDD is in power-save mode, the actuator is rested on the ramp, that is, the head slider is retreated from the magnetic disk to the outside of the magnetic disk.
During a load operation, the head slider is brought down from the ramp onto the magnetic disk. In this process, the head slider is more likely to collide with the magnetic disk since its flying attitude is unstable. Also during an unload operation, the head slider may greatly change its attitude since the head slider is moved quickly over the magnetic disk before the actuator is unloaded on the actuator. However, TFC further increases the possibility of collision between the head element section and the magnetic disk during load/unload since the head element section is protruded as mentioned above.